Concerning theories of justice, law and economics seem to advance along divergent lines: whereas the jurist does not argue any longer for what is "just" nor does he cares about the aim of the law, the economist again gives attention to questions of justice, which is one important subject of "economic philosophy". For a long time the debate about "old" and "new" welfare economics gave the analysis a "welfarist" orientation (I); in this paper we also glance over the main research fields explored nowadays by the economist, all of them being identified with its specific methodological approach: Rawls' "contractualism" gives access to the first "post-welfarist" field, which has renewed normative economics (II). In such a favorable context, Hayek's "evolutionism" receives more attention as a "non welfarist" theory which otherwise could have remained at the margin of the economic thought (III). Lastly, Sen's "comparatism" has become a second "post-welfarist" theory which insists on his complete autonomy towards the first one (IV). Each of these four economics-based approaches can of course be prolonged up to the domain of law.